Polymer materials formed from emulsion polymerization are preferably processed into a powder to accomplish volume reduction, various application and easy handling. In order to obtain powder-type polymer materials formed from emulsion polymerization, latex formed from the emulsion polymerization require to coagulation, aging, dehydration and drying.
Coagulation of emulsion polymerization latex (hereinafter referred to as latex) may be carried out by disturbing, through a chemical method of using various coagulant or a mechanical method of using mechanical force such as strong shearing force, stability of latex particles stabilized by an emulsifier added during emulsion polymerization. In the chemical method, a coagulant type different from an emulsifier type used to secure stability of latex and thus stability is disturbed. When a mechanical method is used to disturb stability, strong shearing force is applied to latex, whereby repulsive force between emulsifiers is overcome and latex particles and other particles are flocculated.
FIG. 1 is a view illustrating an embodiment of a multi-step coagulation process according to conventional technology. Particularly, FIG. 1 illustrates a schematic flowchart in manufacturing equipment of a latex resin powder used in Korean Patent No. 2011-0083024, titled “Polymer slurry having high solid content and method of preparing the same.” The equipment includes largely a latex storage tank 1, a coagulation tank 2, an aging tank 6, a dehydrator 8 and a fluidized bed dryer 10.
In particular, an aqueous coagulant solution 4 is input until the aqueous coagulant solution 4 reaches an upper portion of the coagulation tank 2, and inner temperature thereof is elevated to a coagulation temperature. After a coagulation tank temperature reaches the coagulation temperature, latex in the latex storage tank 1 is transferred and input to the coagulation tank 2. Subsequently, a generated slurry is transferred to the slurry storage tank 7 via the aging tank 6.
Next, dehydration is continuously performed while supplying a slurry to a centrifugal dehydrator 8 using a pump. Here, wastewater 9 generated through dehydration is discarded. A resultant dehydrated slurry along with air is supplied into the fluidized bed dryer 10. The supplied air dehydrates the slurry while moving the same up and down. Dehydrated particles are supplied into cyclone 1 11 by air. At this time, large normal particles 12 fall into a lower portion, and light and small particles are transferred to a cyclone 2 13 and collected as denoted by an arrow 14. Air is released through a line 15. However, when the device is used, it is difficult to stir a slurry having high viscosity and smooth transfer is not exhibited, thereby decreasing powder process efficiency. Accordingly, it is difficult to use a slurry having a high solid content to increase dehydration and drying efficiency, and much time, effort and energy are consumed in subsequent dehydration and drying processes.
In order to enhance such problems, the inventors of the present invention introduced a technology related to a coagulator in which coagulation and aging are simultaneously performed in Korean Patent No. 2013-0159970.
The coagulator in which coagulation and aging are simultaneously performed may include a hollow reaction pipe 160 through which latex passes, one or more barrel pins protruded in an inner side direction of the reaction pipe 160 from an inner wall of the reaction pipe 160, a mixing shaft extended along a center axis of a transfer direction (length direction) of the reaction pipe and one or more stirrers protruding to an inner side of the reaction pipe from an outer side of the mixing shaft, as illustrated in FIG. 2 as a cross-sectional view. Here, a coagulator 100 may be composed of one or more stirrers having non-continuous screws 210.
That is, turbulent flow of latex is induced by substituting at least one of multiple stirrers 150 with the non-continuous screws 210, and thus, a mixing efficiency of a coagulant is increased and a moisture content of a slurry is decreased, whereby subsequent processes such as dehydration and drying are simplified and energy saving effects are accomplished. In addition, the color of an obtained resin powder is enhanced through decrease of the amount of coagulant consumed in a coagulation process and thus quality enhancement effects are provided. A cross section of the reaction pipe 160 may be an arbitrary polygon or a circle, particularly a circle.
The coagulator 100 is designed such that coagulation and aging are performed together, and includes a hollow reaction pipe 160 through which latex passes, one or more barrel pins 140 protruded in an inner side direction of the reaction pipe 160 from an inner wall of the reaction pipe 160, a mixing shaft 170 extending along a center axis of a transfer direction of the reaction pipe 160 and one or more stirrers 150 protruded in an inner wall direction of the reaction pipe 160 from an outer side of the mixing shaft 170. Here, the reaction pipe 160 is composed in a such way that a latex input line 110, a coagulant input line 120 and a steam input line 130 are connected, and latex, a coagulant and steam are supplied into the reaction pipe 160.
The coagulator 100 may include 1 to 20, 4 to 16, or 8 to 12 non-continuous screws 210. Within this range, flow of fluid (non-condensed steam and latex) is disturbed and turbulent flow of latex is induced, and thus a mixing efficiency of steam, latex and a coagulant is increased. However, the non-continuous screws 210 may be disposed in a proper number depending upon the length (L) of the coagulator 100.
The barrel pins 140 extending from the exterior of the reaction pipe 160 to the interior thereof are fixed to the coagulator 100, and the stirrer 150 and/or the non-continuous screws 210 are rotatably fixed to the interior of the reaction pipe 160. In particular, the reaction pipe 160 of the coagulator 100 includes the one or more barrel pins 140 extending to the interior of the reaction pipe 160 from the exterior of the reaction pipe 160. Accordingly, in the reaction pipe 160, latex introduced to the reaction pipe 160 is transferred in a transfer direction when the stirrers 150 and/or the non-continuous screws 210 between the barrel pins 140 fixed to the reaction pipe 160 are rotated, and thus, the latex contacts rotation wings of the stirrers 150 and/or the non-continuous screws 210. The latex collides with the barrel pins 140 through mechanical force generated by such contact, and thus, strong mechanical force, i.e., shearing force is applied to the latex and a stabilized state of latex is disturbed, through a mechanical method, due to an emulsifier added upon emulsion polymerization. Accordingly, coagulation is performed and aging is performed at the rear of the reaction pipe 160.
The shape of the barrel pins 140 may be a circle, a triangle, an inclined shape, an oval shape, a diamond shape, a quadrangle, or the like, and is not specifically limited. In the case of the stirrers 150, any one of a paddle, a screw, a twin screw, a pin, and the like may be used.
The reactor 100 including the non-continuous screws 210 may control a moisture content of latex by providing mechanical force to the latex obtained by the action of the barrel pins 140 and the inner stirrers 150 and/or the non-continuous screws 210.
The coagulator 100 includes the latex input line 110, the coagulant input line 120 and the steam input line 130. Coagulation occurs near a location at which latex, a coagulant and steam are input, and aging is performed in a rear portion of the coagulator. Accordingly, coagulation and aging may be simultaneously performed in one coagulator.
Surface treatment may be performed using a mixer, which induces mixing with a fluid through strong shearing force, such as an in-line mixer. The mixer may be a mixer, in which simple mixing is performed by changing a flow line of a fluid in a pipe, such as a static mixer.
However, even when the coagulator is applied, there are problems due to a remainder of the used coagulant. For example, when a metal ion coagulant is used, thermal stability is enhanced, but moist-heat resistance is decreased due to a remaining metal. When an acidic coagulant is used, moist-heat resistance is enhanced, but thermal stability is decreased due to an acidic remainder.
Accordingly, there is an urgent need for latex powder production technology which may address problems due to a coagulant remainder and simultaneously provide thermal stability secured through application of a metal ion coagulant and moist-heat resistance secured through application of an acidic coagulant.